3.5- Dimethyl-2-cyclohexan

Whilst the solution is still hot, add dilute hydrochloric acid until the stirred solution is just acid to litmus, and then distil off as much ethanol as possible, using the water-bath. Now add more dilute hydrochloric acid to the residual hot solution until it is just acid to methyl-orange. The 5,5-dimethyl-cyclohexan-1,3-dione separates as an oil which solidifies on cooling. Filter the product at the pump, wash it with ice-cold water, and dry it in a desiccator. Yield of the pale cream-coloured crystals, 12 g. m.p. 136-145 (preliminary softening). 

Reactions. The methylene group in the 2 position in 5,5-dimethyl-cyclohexan-i,3-dione (V) is strongly activated by the... 

The most stable conformation of trans 1 4 dimethylcyclohexane has both methyl groups in equatorial orientations The two chair conformations of trans 1 4 dimethyl cyclohexane are not equivalent to each other One has two equatorial methyl groups the other two axial methyl groups... 

Both methyl groups are equatorial m the most stable conformation of trans 1 2 dimethyl cyclohexane... 

Two alkenes undergo hydrogenation to yield a mixture of as and trans 1 4 dimethyl cyclohexane A third however gives only as 1 4 dimethylcyclohexane What compound is this" ... 

The relative amounts of the two products however are not equal more as 1 2 dimethyl cyclohexane is formed than trans The reason for this is that it is the less hindered face of the double bond that approaches the catalyst surface and is the face to which hydro gen IS transferred Hydrogenation of 2 methyl(methylene)cyclohexane occurs preferen tially at the side of the double bond opposite that of the methyl group and leads to a faster rate of formation of the cis stereoisomer of the product... 

Uses. The chemical inertness, thermal stability, low toxicity, and nonflammability of PFCs coupled with their unusual physical properties suggest many useflil applications. However, the high cost of raw materials and manufacture has limited commercial production to a few, small-volume products. Carbon tetrafluoride and hexafluoroethane are used for plasma, ion-beam, or sputter etching of semiconductor devices (17) (see loN implantation). Hexafluoroethane and octafluoropropane have some applications as dielectric gases, and perfluorocyclobutane is used in minor amounts as a dielectric fluid. Perfluoro-1,3-dimethyl cyclohexane is used as an inert, immersion coolant for electronic equipment, and perfluoro-2-methyldecatin is used for... 

A second class of herbicides primarily affects ( -carotene desaturase. These herbicides are apparent feedback inhibitors of PD as well. This class of compounds includes dihydropyrones like LS 80707 [90936-96-2] (56) and 6-methylpyridines (57,58). The third class consists of the ben2oylcyclohexane-diones, eg, 2-(4-chloro-2-nitroben2oyl)-5,5-dimethyl-cyclohexane-I,3-dione. This class of atypical bleaching herbicides induces phytoene accumulation when appHed either pre- or post-emergence. However, it does not inhibit phytoene desaturase activity in vitro (59). Amitrole also has been considered a bleaching herbicide, though its main mode of action is inhibition of amino acid synthesis. 

Cyclohexanedimethanol (47) starts from dimethyl terephthalate. The aromatic ring is hydrogenated in methanol to dimethyl cyclohexane-l,4-dicarboxylate (hexahydro-DMT) and the ester groups are further reduced under high pressure to the bis primary alcohol, usually as a 68/32 mixture of trans and cis forms. The mixed diol is a sticky low melting soHd, mp 45—50°C. It is of interest that waste PET polymer maybe direcdy hydrogenated in methanol to cyclohexanedimethanol (48). 

Obtain energies for diequatorial and diaxial conformers of cis-l,3-dimethylcyclohexane, trans-1,2-dimethyl-cyclohexane and trans-l,4-dimethylcyclohexane. 

How many 13C NMR absorptions would you expect for c/s-1,3-dimethyl-cyclohexane For fra/is-l,3-dimethylcyclohexane Explain. 

Chloro-2,4-dimethyl-cyclohexane (less stable chair form)... 

Bei der Reduktion von tram- und m-(l,2-Dimethyl-cyclohexyl)-cyanamid mit Lithiumalanat werden iiberraschend als Hauptprodukte trans- bzw. cis-1 -Methylamino-1,2-dimethyl-cyclohexan gebildet3 ... 

So erhalt man z. B. aus 6-Oxo-3,3-dimethyl-cyclohexen/Athylendiamin zu 47% d.Th. 4-Oxo-l,1 -dimethyl-cyclohexan [23 Stdn./25° mit Chrom(II)-acetat, Essigsaure, Metha-... 

Nur eine Carbonyl-Gruppe wird bei der Hydrodimerisierung von 1,3-Dioxo- 1,3-diphenyl-propan an Quecksilber reduziert [90% d.Th. 1,6-Dioxo-l,6-diphenyl-hexandiol-(3,4)]9-, analog verhalt sich 3,5-Dioxo-l,l-dimethyl-cyclohexan (Dimedon)10 ... 

In addihon to this so-called 1,3-interaction between an exocyclic substituent and the hydrogens in 3-position, steric interactions can cause extra strain also in 1,2-disubstituted rings as the tra s-l,2-dimethyl-cyclohexane in Fig. 7.10(c). The... 

Fig. 7.10 Examples of equatorial and axial q clohexane substituents and the corresponding energy differences, (a) Methyl-cyclohexane, (b) f-butyl-cyclohexane, (c) frans-1,2-dimethyl-cyclohexane and (d) frans-1,2-dichloro-cyclohexane.

The rate of reaction is markedly solvent-dependent. In the higher-boiling solvents re-octane, ethylcyclohexane, and cfs-1,2-dimethyl cyclohexane the reaction is much faster, but prolonged reflux in these solvents causes extensive decomposition. Some typical results are the following re-octane, 1.75 hours, 64% yield ethylcyclohexane, 2.0 hours, 60% yield. 

It is observed that the 1,3 isomer exists in distereoisomeric cis and transforms. One more thing becomes obvious in the cis form and that is that either both the substituents are equatorial or both are axial. In either case there is a plane of symmetry passing through carbon atoms 2 and 5, if both the substituents are identical, e g., in 1,3 dimethyl cyclohexane. 

Since the rate of opening of the two paths are equal, the enantiomorphs are formed in equal amount. Let us now take another interesting example of 1, 3 dimethyl cyclohexane. It exists in the cis and trans forms. Since the cis form has a plane of symmetry, it is the meso compound. 

Our interest in the forgoing dehydrocyclization mechanisms stems from some superacid-based studies we carried out some years ago, in which an observable cyclodecyl cation 1 loses H2 concomitant with C-C bond formation (shown in bold) to give the 9-decalyl cation 2, and the possible analogy with a 2-octyl cation 3 (as 3 ) giving H2 and 1,2-dimethyl cyclohexane 4 is shown in Scheme 1. The background to this work is reviewed in the next section. 

It is clear that this representation of c/5 -dimethyl-cyclohexane shows a plane of symmetry, and we can deduce it to be a meso compound. No such plane of symmetry is present in the representation of fran -dimethylcyclohexane. Why does this approach work Simply because the transformation of planar cyclohexane (with echpsed bonds) into a non-planar form (with staggered bonds) is a conformational change achieved by rotation about single bonds. The fact that cyclohexane is non-planar means we may have to invoke the conformational mobihty to get the three-dimensional picture. 

When we considered trans- and c -1,2-dimethyl-cyclohexane, we found that only three configurational isomers exist, enantiomeric forms of the trans isomer, together with the cis isomer, which is an optically inactive meso compound (see Section 3.4.5). The meso relationship could be deduced from the plane of symmetry in the hexagon representation. 

Sketch the steps in production of PET from ethane and dimethyl cyclohexanes. 

Perfluoro- 1,3- dimethyl- cyclohexane Perfluoro- n-octane Perfluor- decaline (cis+trans Isomere) Perfluoro- perhydro- phenan- threne... 

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